regressive fallacy

The regressive fallacy is the failure to take into account
natural and inevitable fluctuations of things when ascribing causes to them (Gilovich
1993: 26). Things like stock market prices, golf scores, and chronic back pain
inevitably fluctuate. Periods of low prices, low scores, and little or no pain are
eventually followed by periods of higher prices, scores, pain, etc. To ignore these
natural fluctuations and tendencies leads to self-deception
regarding their causes and to post hoc reasoning.

For example, a professional golfer with chronic back pain or
arthritis might try a copper bracelet on his wrist or magnetic insoles in his shoes. He is
likely to try such gizmos when he is not playing or feeling well. He notices that his
scores are improving and his pain is diminishing or gone. He concludes that the copper
bracelet or the magnetic insole is the cause. It never dawns on him that the scores and
the pain are probably improving due to natural and expected fluctuations. Nor does it
occur to him that he could check a record of all his golf scores before he used the gizmo
and see if the same kind of pattern has occurred frequently in the past. If he takes his
average score as a base, most likely he would find that after a very low score he tended
to shoot not a lower score but a higher score in the direction of his average. Likewise,
he would find that after a very high score, he did not tend to shoot a higher score but
rather would shoot a lower score in the direction of his average.

This tendency to move toward the average away from extremes was
called "regression" by Sir Francis Galton in a study of the average heights of
sons of very tall and very short parents. (The study was published in 1885 and was called
"Regression Toward Mediocrity in Hereditary Stature.") He found that sons of
very tall or very short parents tend to be tall or short, respectively, but not as tall or
as short as their parents.

The professional golfer could check his scores because records
are kept of each game played. Professional golfers frequently are featured in testimonials
for some gizmo guaranteed to improve your golf score. Never does the golfer refer to a
proper study done on golf scores (one which doesn't use optional
starting and stopping) which demonstrates that the improvement, if any,
is not due to natural fluctuation and regression.

Many people are led to believe in the causal effectiveness of
worthless remedies because of the regressive fallacy. The intensity and duration of pain
from arthritis, chronic backache, gout, etc., fluctuates. A remedy such as a chiropractic spinal manipulation or a magnetic belt is likely to be
sought when the pain is at its worst. The pain in most cases would begin to lessen
after it has peaked. It is easy to deceive ourselves into thinking
that the remedy we sought caused our reduction in pain. It is because of the ease with
which we can deceive ourselves about causality in such matters, that scientists do controlled experiments to test causal claims.

Even if a quack remedy does not work, it is often not blamed for
its ineffectiveness. For example, when comedian Pat Paulsen sought "alternative"
medical treatment for cancer in Tijuana, his daughter did not criticize the treatment as
useless when her father died. Paulsen had reportedly had some good days while on the
"alternative" treatments, which would have been expected by natural fluctuation.
His daughter claimed that the treatment worked, but had failed in her father's case
because they had sought the treatment too late. When he was diagnosed with brain and colon
cancer, his wife Noma was quoted in press reports as saying
that the doctor in Tijuana "is confident it can be cured. The doctors here
say it can't. We like the ones over there a lot better." An official press release on
his death claimed he died from pneumonia, not cancer. A family spokesman was quoted as
saying: "His cancer was under control after undergoing alternative treatment in
Mexico. He succumbed at 2pm on Thursday after complications brought on by pneumonia and
kidney failure after recent non-cancer related surgery." His wife did not think the
alternative therapy was worthless. She said: "We want to thank our team of doctors in
Mexico who treated my husband humanely and with respect, and who were with him 24 hours a
day trying to save his life."*